Worms Are Eating the Rose Leaves and Buds

Damage caused by caterpillars and rose slugs is often minimal.

Worm-like insects chewing rose leaves and buds are most likely caterpillars or rose slugs, the larvae of moths and butterflies or sawflies, respectively. Roses (Rosa spp.) are generally hardy across U.S. Department of Agriculture plant hardiness zones 6 to 10, but cold-tolerant species and varieties are often hardy to zone 3. Caterpillars and rose slugs appear in the warmer months of spring and summer and many species find roses attractive food sources. Use an integrated pest management approach to control them, relying on cultural and organic methods and, if necessary, pesticides.

Worm-like Pests

Common types of caterpillars that frequent roses include orange tortix larvae, tussock moth larvae, leaf-rollers, tent caterpillars, corn earworms, tobacco budworms, loopers and bollworms. Many of these species are members of the silkworm family. Other worm-like larvae that feed on roses include several types of rose slugs. Many of these appear as tiny green or yellow-green worms, often found on the undersides of leaves, but will gnaw on leaves, buds and blooms alike.

Types of Damage

The hallmarks of caterpillar damage are oblong holes chewed throughout the center or along the edges of leaves, gnawed-out holes bored through the bottoms of buds, or bud tips that have been partially chewed. Rose slugs tend to skeletonize leaves, eating the tender parts between leaf veins but may cause damage that resembles that of caterpillars as they mature. The presence of rolled leaves with web-like silk attachments is a good indicator of caterpillar activity. In most cases, damage is usually aesthetic in nature, rarely threatening the health of the roses.

Cultural & Biological Controls

Many types of rose slugs and caterpillars can be hand-picked and destroyed if infestations are small and plant damage is limited. Leaves that show evidence of rolling can likewise be pinched off and destroyed. Sawflies, along with some moths and caterpillars, may lay their eggs on rose leaves in early autumn, where they remain dormant until the next spring. Thoroughly clean up leaf litter before winter to minimize egg-harboring foliage. Also, many birds enjoy feasting on caterpillars and rose slugs. Encouraging their presence in your garden with nesting sites, feeders and water sources can cut down on populations of these pests.

Insecticides

Organic insecticides that are generally effective against caterpillars and slugs include pyrethrin, which is derived from a type of chrysanthemum plant, neem oil, extracted from the tropical neem tree and Bacillus thuringiensis, or Bt., a type of bacteria that easily infects and kills caterpillars. Insecticidal soaps are also effective when caterpillars and rose slugs are small. Synthetic alternatives include sprays, powders and root treatments like carbaryl, permethrin, malathion and combination products. Only use broad-spectrum, synthetic insecticides in the case of severe infestations. Apply them in the early evening, to avoid injuring or killing beneficial bees, which are most active during daylight hours.

About the Author

Lynn Cochran is a professional writer and contributing author to the educational website, Gardening Carolina. He also volunteers as a North Carolina Master Gardener. He is educated in environmental science, botany, health care and English literature. He is currently pursuing an accelerated master's degree in applied geography at the University of North Carolina at Greensboro.